Merging python-backend

DIGEST: - New Python2 backend for Cantor:
* Python2 backend working with python2.x series;
* Syntax highlighting;
* Tab-complete;
* Help panel;
* Variable management panel;
* Dynamic keywords support;
* Compatible with several(all?) python2 modules;
* Allow appen python2 plot image in Cantor workspace.

- New packaging extension:
* Extension for import library/module for backend

Conflicts:
src/backends/scilab/CMakeLists.txt